In a wireless communication system, a sender and a receiver achieve higher rates in a spatial multiplexing manner by virtue of multiple antennae. The receiver needs to perform channel measurement according to a pilot signal sent by the sender and feeds back channel information to the sender, and the sender uses some sending pre-coding technologies according to obtained CSI to greatly improve transmission performance. In a Long Term Evolution (LTE) system, channel information is obtained by measuring and estimating channel according to a Cell specific Reference Signal (CRS) or a Channel State Information Reference Signal (CSI-RS). In a newer protocol version, CSI-RS-based channel measurement is mainly adopted.
In a related art, a NodeB may periodically send one or more sets of CSI-RSs, and a terminal uses these CSI-RSs for channel measurement, and then feeds back CSI to the NodeB. The CSI-RS is significant for performance of a Multiple Input Multiple Output (MIMO) system. Generally, each antenna sends one channel measurement pilot signal. Locations of channel measurement pilot signals sent by different antennae in the time and frequency domains or the code domain are staggered, and may be kept orthogonal without mutual interference, and each antenna corresponds to one CSI-RS port. The terminal may measure physical channels between its receiving antennae and sending antennae at a receiver, thereby obtaining an Nr*Nt channel matrix, wherein Nr is the number of the receiving antennae, and Nt is the number of the sending antennae.
A location of a subframe for sending a CSI-RS in the time domain and a location of a Resource Element (RE) in the subframe are introduced below. In the time domain, a channel may not be suddenly changed, and each subframe is only 1 ms, so that it is unnecessary to send all subframes. A CSI-RS may be shared by all User Equipment (UE), so that the CSI-RS is periodically sent under a normal circumstance. Regulations in standard 36.211 of LTE are shown in Table 1, i.e. CSI-RS subframe configuration.
TABLE 1CSI-RSCSI-RS subframe offsetCSI-RS-SubframeConfigperiodicity TCSI-RSDeltaCSI-RSICSI-RS(subframes)(subframes)0-45ICSI-RS 5-1410ICSI-RS-515-3420ICSI-RS-1535-7440ICSI-RS-35 75-15480ICSI-RS-75
In table 1, ICSI-RS is a configuration parameter of a CSI-RS, and is valued from 0 to 154, and different values may correspond to different CSI-RS periodicities and subframe offsets. FIG. 1 is a diagram of locations of subframes corresponding to a part of CSI-RS configuration examples, the subframe locations corresponding to the configurations of ICSI-RS=0, ICSI-RS=2 and ICSI-RS=5 respectively.
At a frequency-domain location, there is a CSI-RS in each Physical Resource Block (PRB) pair, and a sending pattern of the same port in different PRB pairs is the same. A pattern of a CSI-RS is shown in FIG. 2. A PRB pair may refer to a regulation in LTE protocol 36.211, and a typical condition includes 12 frequency-domain subcarriers and 14 time-domain Orthogonal Frequency Division Multiplexing (OFDM) symbols.
An LTE system defines that 40 REs in one PRB pair may be used as CSI-RSs and are divided into 5 patterns, and each pattern includes 8 REs, as shown in the FIG. 1. Each port of the CSI-RS averagely occupies one RE in one PRB pair, and all the ports belonging to the same CSI-RS resource are required to be limited in one pattern. At present, one set of CSI-RSs may support maximally 8 ports, so that there are five location candidates when the number of the ports is 8, there are 10 configurable locations when the number of the ports is 4 and there are 20 configurations when the number of the ports is 2.
In the related art, a CSI-RS is a Cell/Transmission Point (TP) specific design, a NodeB is not allowed to perform pre-coding processing when sending a CSI-RS, and it is mainly because the CSI-RS is shared by multiple pieces of UE in a cell, the CSI-RS may be pre-coded only according to a characteristic of a channel between the NodeB to one piece of UE if it is necessary to pre-code the CSI-RS, which may cause influence on the measurement of the other UE and disable the other UE to accurately measure physical channels between Nr receiving antennae and Nt sending antennae, and pre-coding according to characteristics of channels of the other UE may make it impossible to accurately calculate and report own CSI.
In addition, the CSI-RS is periodically sent in the related art. At present, maximally 8 antennae are supported, so that overhead in the CSI-RS is not so high. However, for a condition of more antennae, pilot overhead of such a method may be greatly increased along with multiplication of the number of the antennae, which may cause influence on spectrum efficiency of a system.
Moreover, corresponding to a high-dimensional CSI-RS, CSI calculation may be more complex, terminal complexity is high and time consumption in CSI calculation is higher.
Therefore, the following major problems exist in the related art: a CSI-RS is periodically sent, so that overhead is higher, and resources are wasted; the CSI-RS is cell/TP specific, so that pre-coding is not allowed, and the number of ports may not further be effectively reduced; and when there are more antennae, the overhead is high, and CSI feedback is large in calculation amount and high in complexity.